The invention relates to a method of manufacturing a cathode ray tube from a neck part and a cone part.
U.S. Pat. No. 4,217,521 discloses a television picture tube having a resistive coating which is deposited on an outer area of the tube and is in contact with a conductive coating to disperse any static charges by means of a flow of electrons through the resistive coating. The xe2x80x9crushxe2x80x9d of electrons is attenuated thereby and thus suppresses an annoying crackling sound taking place upon tube turn-on and turn-off. Furthermore, any residual high-potential charges remaining after turn-off are discharged to ground.
Conventionally, the neck part and the cone part are first connected to each other during manufacture of such a television picture tube, while the resistive coating is applied in a later phase of the manufacturing process. Initially, i.e. before the connection step has taken place, the cone part is closed at a side that is to be connected to the neck part: the so-called xe2x80x9cstubxe2x80x9d. During the connection step, this stub is removed, whereafter the cone part and the neck part are connected to form a tube assembly. In a later phase of the tube manufacturing process, the coating is applied e.g. by brushing or spraying the tube assembly with a suspension of the coating and subsequent drying of the coating.
The conventional way of manufacturing such a television picture tube has the drawback of being a complex process in view of the required steps of controlling the electrical and mechanical coating properties. Furthermore, these measures are not always fully effective and increase the cost price of the tube.
It is an object of the invention to provide a method of manufacturing a display device that does not have the above-mentioned drawback. To this end, the invention is characterized in that the method comprises the steps of: coating an external surface of the cone part with a coating, and subsequently connecting the cone part to the neck part.
The inventors have realized that, if the order of processing is reversed, i.e. first applying the coating to the cone part and then connecting the neck part and the cone part, the required measures for controlling the coating properties may be substantially reduced. In the method according to the invention, the cone part is first provided with the coating by immersing it into a bath containing the suspension of the coating. Due to the presence of the stub, the inner part of the cone part remains free from the coating. The cone part and the neck part are connected by first removing the stub and then connecting the cone part and the neck part together in the conventional way.
Advantageous embodiments of the invention are defined in the dependent claims.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.